dotard (n.)

late 14c., "imbecile, one who is in dotage or second childhood;" see dote (v.) + -ard. Sense of "one who dotes, one who is foolishly fond" (c. 1600) is now rare or obsolete. Other noun derivatives of dote, all in the sense "fool, simpleton" in Middle English were dotel (late 14c.), doterel (late 15c.), doti-poll (c. 1400; see doddypoll).